Lipophilic skin care active agents such as retinoids are generally applied topically to reduce the appearance of aging, for other cosmetic purposes, or to treat a skin condition such as acne.
The comfort associated with application of topical agents is related in part to the rate of evaporation of the applied composition on the skin. A product with a slow evaporation rate could feel greasy on the skin whereas a product with an overly rapid evaporation rate feels either as if it has not been applied to the skin at all or leaves the user with the impression that not enough has been applied possibly leading to overuse. Combining topical agents with volatile silicones allows the proper evaporation rate to provide a pleasing application. Silicones, however, by themselves are poor solvents for hydrophobic organic active agents.
To address the poor solubility in silicones, delivery systems for these agents commonly require 35% or more organic solvent as a carrier to solubilize the active agent as well as provide suitability for combination with volatile compounds that provide pleasing application by the user. The prior art prefers alcohols such as ethyl alcohol as an organic solvent.
Many active agents contribute to thinning or drying of the skin. This problem is worsened by including significant levels of organic solvents that themselves can alter epidermal barrier lipids and contribute to skin irritation. Ethyl alcohol as used in the retinoid composition of U.S. Pat. No. 4,826,828 was believed to be the solution for topical delivery of hydrophobic agents. Ethyl alcohol, to the contrary, contributes to skin irritation and dryness. Thus, combining ethyl alcohol with potentially irritating active agents increases skin dryness leading to non-optimal use.
Thus, there exists a need for a hydrophobic active agent delivery system that provides pleasing application and does not contribute to toxicity.